The present invention relates to a macro-adapted zoom lens system capable of high zoom ratio and which covers wide angles. More particularly, the present invention relates to a macro-adapted zoom lens system for a 35 mm still camera that comprises a positive, a negative, a positive and a positive lens group and which can be adjusted from the wide-angle position to the telephoto end.
Conventional zoom lens systems capable of high zoom ratio and which cover wide angles achieve focusing by two methods. The one method, which has been known for many years and may be described as the old method, depends on the first lens group for focusing purposes. The other method, which has been made known in recent years and hence may be named a new method, is applicable to a five-group type zoom lens system comprising a positive, a negative, a positive, a negative and a positive lens group. In this new method, focusing is achieved either by displacing the first and second lens groups in unison, or by displacing the third, fourth and fifth lens groups in unison.
In focusing by the new method, it is fairly easy to reduce the minimum distance at which closeup shooting can be made. However, if the old method of focusing is directly applied to a zoom lens system capable of high zoom ratio and which covers wide angles, the quantity of light admitted at the widest angle position (i.e., at the shortest focal length) is so much decreased that it is very difficult to reduce the minimum distance at which closeup shooting can be made.
As mentioned above, zoom lens systems that employ the old method to achieve focusing have the disadvantage that the minimum distance at which closeup shooting can be made is rather long, so in order to provide for closeup shooting at a nearer distance, various macro-adapted systems have been invented and used in practice. Such macro-adapted lens systems include:
(i) a system in which all the lens groups used are advanced to achieve zooming; PA0 (ii) a system in which the first lens group is advanced from the shortest-distance shooting position at the narrow angle mode (or including the middle-angle mode); and PA0 (iii) a system in which part of the lens groups such as, for example, the second lens group, is advanced toward the object side at the narrow- angle end.
These systems, however, have the following disadvantages:
(i) This is optically the simplest lens system but mechanically it is complex and bulky and the user finds it troublesome to displace all the lens groups which are unpleasantly heavy en masse;
(ii) This is mechanically the simplest lens system but it suffers the disadvantage that the first lens group has to be moved by an unduly large amount and that an undercompensated spherical aberration and an overcompensated field of curvature will develop at a maximum magnification of the image in a macro mode, thereby causing undesirably great aberrational variations (see FIG. 3);
(iii) This system has the advantage that the required amount of lens displacement is small and that it is simple in construction, but it is subject to great deterioration in performance.